The following HD-DVDs are available from HMV for £4.99 a pop inclusive (before Quidco):
Flags of Our Fathers
Harry Potter and the Philosopher's Stone
Harry Potter and the Chamber of Secrets
Harry Potter and the Goblet of Fire
Harry Potter and the Order of the Pheonix
Harry Potter and the Prisoner of Azkeban
Letters From Iwo Jima
(All 5 Potter films for £22.50 after Quidco. £24.95 without Quidco)
When using the link, click on "HD-DVD (70)" in the left hand menu (this is the list of the 70 Warner HD-DVDs HMV sells). Then sort by price.
These films aren't showing up on the HD-DVD specials page, so you'll have to search for them using the search feature on the website. Go through Quidco to get another 10% back. Some are now showing as out of stock, but with stock expected in within 7 days. These titles are also available from The Hut and Asda Entertainment, but from personal experience you're more likely to actually get them from HMV! About time the Warner titles started dropping in price! I think most people have all the Universal titles they want now.